This invention relates to metallic coatings for metal articles prone to corrosion, and, more specifically, to an industrial metallic roll coating with abrasion resistant and release properties that has no through grain porosity.
Metallic roll coatings with abrasion resistant and release properties have in the past been produced using a porous plasma type or wire type flame spray plated based layer and an impregnated Teflon.RTM. film top coat. It is believed that the through grain porosity in the plating has not offered completely adequate corrosion resistance in some cases. In fact, older processes such as wire type or plasma type flame spray plating processes are deficient because they do not result in through grain sealed properties, rather they are regarded as porous.
A known process for producing a composite metallic roll having a release surface is disclosed in U.S. Pat. No. 3,942,230 to Nalband. Nalband discloses application of a porous nickel chromium alloy (or other metal) by a flame spray process. Upon the resulting porous metal layer is deposited a fluorocarbon polymer (Teflon.RTM.), which is subsequently heated so as to impregnate and cover the porous layer.
In Nalband and other known coating processes, the Teflon layer only provides a corrosion barrier ancillary to the Teflon's principle function of providing a release surface. In recent years, however, operating conditions in industries such as the production of pulp and paper and plastics have generated significantly more demanding requirements in respect to corrosion resistance which are not necessarily within the capabilities of Nalband and other previously known processes.